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Kepler-78b is a planet that shouldn’t exist. This scorching lava world circles its star every eight and a half hours at a distance of less than one million miles — one of the tightest known orbits. According to current theories of planet formation, it couldn’t have formed so close to its star, nor could it have moved there.

Kepler-78b is a planet that shouldn’t exist. This scorching lava world, shown here in an artist’s conception, circles its star every eight and a half hours at a distance of less than one million miles. According to current theories of planet formation, it couldn’t have formed so close to its star, nor could it have moved there. (Credit: David A. Aguilar (CfA))

“This planet is a complete mystery,” says astronomer David Latham of the Harvard-Smithsonian Center for Astrophysics (CfA). “We don’t know how it formed or how it got to where it is today. What we do know is that it’s not going to last forever.”

“Kepler-78b is going to end up in the star very soon, astronomically speaking,” agrees CfA astronomer Dimitar Sasselov.

Not only is Kepler-78b a mystery world, it is the first known Earth-sized planet with an Earth-like density. Kepler-78b is about 20 percent larger than Earth, with a diameter of 9,200 miles, and weighs almost twice as much. As a result it has a density similar to Earth’s, which suggests an Earth-like composition of iron and rock.

May 30, 2013 — Detailed analysis and review have borne out researchers’ initial interpretation of pebble-containing slabs that NASA’s Mars rover Curiosity investigated last year: They are part of an ancient streambed.

NASA’s Curiosity rover found evidence for an ancient, flowing stream on Mars at a few sites, including the rock outcrop pictured here, which the science team has named “Hottah” after Hottah Lake in Canada’s Northwest Territories. It may look like a broken sidewalk, but this geological feature on Mars is actually exposed bedrock made up of smaller fragments cemented together, or what geologists call a sedimentary conglomerate. Scientists theorize that the bedrock was disrupted in the past, giving it the titled angle, most likely via impacts from meteorites. (Credit: NASA/JPL-Caltech/MSSS)

The rocks are the first ever found on Mars that contain streambed gravels. The sizes and shapes of the gravels embedded in these conglomerate rocks — from the size of sand particles to the size of golf balls — enabled researchers to calculate the depth and speed of the water that once flowed at this location.

“We completed more rigorous quantification of the outcrops to characterize the size distribution and roundness of the pebbles and sand that make up these conglomerates,” said Rebecca Williams of the Planetary Science Institute, Tucson, Ariz., lead author of a report about them in the journal Science this week. “We ended up with a calculation in the same range as our initial estimate last fall. At a minimum, the stream was flowing at a speed equivalent to a walking pace — a meter, or three feet, per second — and it was ankle-deep to hip-deep.”

ScienceDaily (Oct. 12, 2012) — The first Martian rock NASA’s Curiosity rover has reached out to touch presents a more varied composition than expected from previous missions. The rock also resembles some unusual rocks from Earth’s interior.

Target: Jake Matijevic Rock. This image shows where NASA’s Curiosity rover aimed two different instruments to study a rock known as “Jake Matijevic.” (Credit: NASA/JPL-Caltech/MSSS)

The rover team used two instruments on Curiosity to study the chemical makeup of the football-size rock called “Jake Matijevic” (matt-EE-oh-vick). The results support some surprising recent measurements and provide an example of why identifying rocks’ composition is such a major emphasis of the mission. Rock compositions tell stories about unseen environments and planetary processes.

“This rock is a close match in chemical composition to an unusual but well-known type of igneous rock found in many volcanic provinces on Earth,” said Edward Stolper of the California Institute of Technology in Pasadena, who is a Curiosity co-investigator. “With only one Martian rock of this type, it is difficult to know whether the same processes were involved, but it is a reasonable place to start thinking about its origin.”

ScienceDaily (Sep. 14, 2012) — NASA’s long-lived rover Opportunity has returned an image of the Martian surface that is puzzling researchers.

Small spherical objects fill the field in this mosaic combining four images from the Microscopic Imager on NASA’s Mars Exploration Rover Opportunity. (Credit: NASA/JPL-Caltech/Cornell Univ./ USGS/Modesto Junior College)

Spherical objects concentrated at an outcrop Opportunity reached last week differ in several ways from iron-rich spherules nicknamed “blueberries” the rover found at its landing site in early 2004 and at many other locations to date.

Opportunity is investigating an outcrop called Kirkwood in the Cape York segment of the western rim of Endeavour Crater. The spheres measure as much as one-eighth of an inch (3 millimeters) in diameter. The analysis is still preliminary, but it indicates that these spheres do not have the high iron content of Martian blueberries.

“This is one of the most extraordinary pictures from the whole mission,” said Opportunity’s principal investigator, Steve Squyres of Cornell University in Ithaca, N.Y. “Kirkwood is chock full of a dense accumulation of these small spherical objects. Of course, we immediately thought of the blueberries, but this is something different. We never have seen such a dense accumulation of spherules in a rock outcrop on Mars.”

The Cassini spacecraft has been busy over this past week, making close flybys of both Enceladus and and Tethys, two of Saturn’s moons. And we’re not using “close” as a relative term here. Cassini skimmed Enceladus in such proximity that it was literally able to taste the plume of water ice, vapor, and other organic compounds spewing from the moon’s south polar region.

That flyby was at an altitude of just 46 miles above Enceladus’s surface, a hair’s breadth as these sorts of things go. Unfortunately for us, Baghdad Sulcus–the fracture from which said plume emanates–is in darkness for this flyover, but Cassini was able to snap various high-res surface shots of the moon as it passed back into daylight.

Enceladus at the Surface: NASA/JPL/Space Science Institute

For its Tethys encounter, Cassini took a bit more conservative approach, passing about 5,700 miles above the moon’s surface. It was the first imaging expedition to Tethys since 2005, when Cassini captured imagery from its Saturn-facing side. This time Cassini snapped views of Tethys’s other side, which should provide researchers with enough data to start building decent digital elevation maps of Tethys’s surface.